Protective helmets worn by pilots are generally provided with one or more visors which can be moved between lowered positions in front of the wearer's eyes and raised positions clear of his field of vision. Many and various mechanisms are known in the prior art for actuating helmet visors to permit the visor to be held in discrete positions between the raised and lowered positions. Other assemblies permit the visor to be moved into and held in any position intermediate to the raised and lowered positions.
Higgs U.S. Pat. No. 4,170,792 shows a mechanism which is especially adapted for use in connection with the visors on a pilot's helmet or the like. More particularly, it shows an arrangement in which a clutch output member carried by the visor is rotatably supported on a cylindrical boss secured to the helmet shell. A cutout in the clutch output member receives a pair of rollers which are urged by respective springs toward the central reduced diameter portion of the cutout to wedge the rollers between the boss and the clutch output member. A knob rotatably supported on the boss carries a clutch release element of tang disposed between the rollers and adapted to be moved into engagement with one or the other of the rollers to move it against the action of its spring to a relatively larger diameter portion of the cutout to release the visor for movement with the knob to an adjusted position in which it is again locked by the rollers.
While the arrangement shown in Higgs provides infinite adjustment of the position of the visor and a relatively positive locking action, the operation of the device is not as smooth as is desirable. More specifically, if the visor is in the up position and a person wearing the helmet actuates the knob to move the visor down, after the roller which had been holding the visor in the up position is moved to the release position, the weight of the visor itself causes the visor to get ahead of the wearer's movement of the knob so that the visor moves down in a number of steps. Stated in another way, in the course of the wearer's movement of the knob from the up position to the desired down position, the visor falls down a short distance under the action of gravity, is locked again, is unlocked, and moves down another short distance under the influence of gravity until it finally stops in the desired down position. Clearly, this operation is undesirable.
Application Ser. No. 07/766,754 of Hedges et al filed Sep. 27, 1991, now U.S. Pat. No. 5,230,101 discloses an arrangement for overcoming the problem discussed above. In the structure disclosed therein, each of the visor assemblies is provided with a drag ring which prevents the irregular movement of the visor in going to the down position, as discussed hereinabove.
Mechanisms of the type shown in the Higgs patent and in the Hedges et al application have the advantage that any force exerted directly on the visor only increases the force with which the locking roller or rollers is wedged. Thus any force, such as windblast encountered by the visor, only results in the visor being locked more securely.
It has now been discovered that mechanisms of the type described hereinabove incorporate another defect. As has been pointed out hereinabove, mechanisms of this type lock tighter and tighter in response to an opposing force such as occasioned by windblast and the like. While this function itself is desirable, it results in what is at least an inconvenience to the user in that a variable force may be required to unlock the mechanism and move the visor. For example, if an attempt is made to move the visor up by rotating the knob after the visor has been subjected to windblast in the up direction, the force with which the roller is wedged is so great that the force exerted by the actuator or tang on the roller merely tends to drag everything along, including the visor. This tendency can be overcome by holding the visor stationary or even moving it in the other direction while turning the knob. Clearly, such a two-handed operation is anathema to the pilot who has many other concerns to occupy him. Users such as aircraft pilots cannot develop a routine which would be instinctive. Stated otherwise, at high speeds and low altitude, the pilot has other things on his mind than the procedure which may be required to release the visor locking mechanism.